-LRB- CNN -RRB- More than 500 Houthi rebels have been killed since the start of Saudi-led military operations against Yemeni Shia fighters , a Saudi Defense Ministry official said Saturday , according to the state-run Saudi Press Agency .

A Saudi general said Saturday the nine-nation coalition has undertaken 1,200 airstrikes since they began on March 26 .

Gen. Ahmed Asiri added that the raids aim to keep the rebels from moving toward southern Yemen , according to the SPA .

Clashes took place Friday near the Saudi-Yemeni border , in the Najran region . Saudi forces responded to mortar rounds fired by Houthis on a Saudi border site .

Three Saudi military officers were killed and two others were wounded in the shelling , a defense official said , according to SPA .

A Saudi source also confirmed to CNN 's Nic Robertson that three Saudi soldiers were killed in the shelling .

The Yemeni Health Ministry on Saturday said 385 civilians have been killed and 342 others have been wounded . The World Health Organization has put higher figure on both tolls -- 648 killed and 2,191 wounded -- but includes militant casualties in the totals .

Yemen has been descending into chaos in the weeks since Houthi rebels -- minority Shiites who have long complained of being marginalized in the majority Sunni country -- forced Yemeni President Abdu Rabu Mansour Hadi from power in January .

And even before the crisis escalated with the Saudi airstrikes , most of the 25 million people in Yemen required humanitarian assistance to meet their most basic needs , the United Nations said Friday .

CNN 's Pierre Meilhan and Mohammed Tawfeeq contributed to this report .

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Saudi general says more than 1,200 airstrikes since campaign began March 26

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Three Saudis were killed in attack on border position , source tells CNN